FR2781791A1 - PROCESS FOR MANUFACTURING PARTS OF COMPOSITE MATERIALS REINFORCED WITH FIBERS - Google Patents

Abstract

a) Method for manufacturing ceramic parts with internal structure and in particular with internal passages. b) A method characterized by the fact that at least one metal core (20) consisting of silicon or a silicon alloy is added which is introduced to the press in the blank and remains there and serves as a source of silicon during infiltration by a melt bath. c) The invention makes it possible in particular to manufacture ceramic brake discs allowing internal ventilation of the disc.

Description

I

  METHOD FOR MANUFACTURING PARTS OF MATERIALS

ARMORED FIBER COMPOSITES.

  The present invention relates to a method for manufacturing parts made of fiber-reinforced composite materials from raw parts armed with fibers, having a porous carbon matrix based on carbon, in particular from ceramic / ceramic C / C composite parts, in the case of which fibers, bundles of fibrous material or fiber agglomerates based on carbon, nitrogen, boron and / or silicon are mixed, with at least one carbonisable binder and possibly other addition materials or fillers for obtain a mass to be pressed and the mass to be pressed is pressed to obtain a blank, which is then pyrolyzed, the binder, of which there is at least one, converting into a matrix based on porous carbon and the raw part, army of fibers, resulting

  being infiltrated with a molten metal or silicon.

  The process according to the invention relates in particular to the manufacture of composite ceramic materials as well as composite ceramic materials reinforced with fibers. It infiltrates a porous pre-ceramic part with a metal or

  silicon, Metal or liquid silicon is deposited there in the pores.

  In the case of the infiltration by silicon of carbon-based preceramic parts, the reaction gives rise to silicon carbide which is the ceramic proper. This process is for example

  described in document DE 44 38 455 Cl.

  This process is used in particular during the manufacture of ceramic brake discs. In this regard, the production of internally ventilated brake discs poses problems. It is very difficult to obtain ventilation channels in solid ceramic discs, because the material is very refractory and difficult to machine. When obtaining channels in pre-ceramic blanks, problems may arise because, depending on the circumstances, the geometrical characteristics of the part and its dimensions may be changed as a result of

infiltration of the melt.

  The object of the invention is therefore to provide a method of the type mentioned above with which it is possible to manufacture ceramic pieces having internal structures,

  especially channels and the like.

  The solution lies in the fact that at the blank, at least one core containing a metal or silicon content is added which, during the infiltration of the melt, is used as a source of metal or

of silicon.

  The process according to the invention, with which the pre-ceramic parts are infiltrated by a fusion bath using cores with a metal or silicon content, the cores serving as a source of metal for the silicon, has the advantage that the we can manufacture in the simplest way, with high dimension accuracy, parts

composites with internal structure.

  A variant of the present invention provides for the production of pre-ceramic parts or blanks with internal structures, the cores being inserted into these structures before the infiltration of the molten bath. A second embodiment consists in applying the internal structure, in particular the ventilation channels, during the pressing of the blank, in the form of silicon metal content cores which remain in place until the 'infiltration of the melt. It is therefore possible to envisage both cores serving as a source of pure silicon as cores operating, for example during the manufacture of ventilated brake discs, as a ventilation core in the form of a lining inserted as tooling. According to the invention, preferably technically pure metal or silicon cores are used. Another advantageous extension provides for the use of a mixture of silicon and boron nitride. A third advantageous extension consists of the use of alloys, in particular silicon / iron alloys or silicon / aluminum alloys. These cores can be made by casting or pressing. Manufacturing can be done under protective gas. A shielding gas is necessary during the melting of the silicon, before the fabrication of the core itself. Silicon cores ranging from very pure to technically pure can be manufactured by casting. A preferred method of manufacturing the core is the firing of the core, as it applies for example during the manufacture of the sand core in the casting technique. Silicon / boron nitride mixtures or alloys of silicon with other metals can be cast, lowering the melting point relative to the pure components being advantageous. They can also be made

  by extrusion or by die casting.

  It can also be obtained by milling, after pressing

  the blank, the channels to be filled with cores.

  Another advantageous extension provides that a blank containing cores with a metal or silicon content is obtained on a flywheel press, from a pressing mass containing one or more cores. The fibers contained in the mass to be pressed are then oriented along the metal or silicon content core according to the direction of the force. The resulting ceramic part has the typical characteristics of a ceramic, namely rigidity and high resistance to wear. These characteristics

  particularly suitable for brake discs.

  An embodiment of the present invention is described in detail below with the aid of the accompanying drawings: FIG. 1a is a schematic section of a device for pressing a pre-ceramic formed part containing a core containing silicon ; before (on the right) and after (on the left) insertion of the core, figure lb represents the device of figure la after the pressing process; Figure 2 is a schematic sectional view of a pre-ceramic shaped part that can be obtained with the device of Figures la and lb. Figure 3 shows another embodiment of a

  pre-ceramic shaped part containing a silicon-containing core.

  To manufacture a pre-ceramic part formed from a mass to be pressed, a conventional pressing device can be used. The press material contains fibers or bundles of fibrous material made of silicon, carbon, boron and / or nitrogen fibers with a binder suitable for pyrolysis, other binders, and fillers. The fibers or bundles of fibrous materials can be impregnated with a binder suitable for pyrolysis and / or coated with pyrolytic carbon. This mass is pressed to make a blank. Then the blank is carbonized (pyrolyzed) under vacuum or under protective gas to manufacture a porous piece formed with carbon content which is infiltrated with a

silicon fusion bath.

  The pressing device used may have cores which are integral with the interior surface of the pressing device. However, the cores can also be mobile, for example being arranged hydraulically in the pressing device. The cores are inserted into the mass to be pressed. The cores can also be introduced into the pressing device, leaving them free. After pressing the blank, the cores are extracted, which results in a blank with through holes. In these through holes, cores are plugged in which are made of very pure or technically pure silicon, a mixture of silicon and boron nitride or an alloy containing% silicon and 40% iron or 60% silicon and 40% aluminum. It is carbonized and then silicified, in a process with

  a single step, the resulting blanks, filled with these cores.

  One can for example pour the cores of pure silicon by placing them in a mold, coated with boron nitride, which is then filled with liquid silicon. After solidification, the finished cores can be removed. One can for example manufacture by core firing or by isostatic pressing of the cores consisting of a mixture of silicon and boron nitride, optionally with the addition of a binder. It is also possible to manufacture a pasty mass of silicon, boron nitride and one or more binders and to obtain cores by extrusion, in a manner comparable to the extrusion of plastics, known per se. Cores can be made from an alloy, for example by melting or pressing a metal powder with a proportion of about 5 to 20% by weight of binder. In principle, care should be taken that the silicon content of the cores is sufficient for each

  complete penetration of the pre-ceramic part formed to infiltrate.

  Those skilled in the art can calculate for each particular case the degree of purity or the silicon content since it is possible to know the volume of the channels of the blank as well as to calculate the silicon requirement for infiltration by the fusion bath. The manufacturing of the core can be done under protective gas, the melting of the

  silicon to be done under shielding gas.

  Next, the blank provided with plugged silicon cores is subjected to infiltration by known fusion bath. Then, the silicon contained in the cores melts and penetrates into the porous pre-ceramic parts, a transformation taking place with the carbon contained in the pre-ceramic part formed to give

  the silicon carbide ceramic material.

  Figures la and lb show a device for pressing a preceramic part formed with a core containing silicon. The device 10 has an upper punch 11 (FIG. 1b) and a lower punch 12. The lower punch 12 also has an inner punch 13 which can be moved vertically by means of a hydraulic lifting device 14. Furthermore, the lower punch 12 is provided with a "flying envelope" 15 which can also be moved vertically by means of a

hydraulic lifting 16.

  The intermediate mass located between the inner wall of the flying envelope 15 and the inner wall of the inner punch 13 is filled with pressing material 30 (FIG. 1a to the right). Next, a shaped core is placed in the device 10. of star 20 consisting of silicon or boron nitride or an alloy with a silicon content. This star-shaped core 20 can be made as described above. The core is placed so that its outer edge a rests on the inner face of the flying envelope 15 and its inner edge 20b on the inner punch 13. The inner punch 13 and the flying envelope 15 then fade a little towards down on

  along their lifting device 14 or 16 (figure la, on the left).

  Both the flying envelope 15 and the inner punch 13

  may be provided with receptacles 15 ′ or 13 ′ for the core 20.

  Next, an annular lining 17 is placed on the flying envelope 15 and on the outer edge 20a of the core 20 (figured on the left). The ring 17 is filled with additional pressing mass 30. Then the upper punch It is lowered and the pressing mass 30 is pressed to give a blank, the flying envelope 15 and the inner punch 13 moving fully vertically down

(figure lb).

  The pre-ceramic formed part 40, finished, containing the core in

  star shape 20, is shown diagrammatically in FIG. 2.

  It is then subjected in a known manner to pyrolysis and to infiltration by a melt. Then, the star-shaped core 20 melts, the silicon penetrates into the pores of the pre-ceramic formed 40 and forms therein silicon carbide. There remains a ceramic part having through holes, the shape of which corresponds with a precision of dimension high to that of the core in

star shape.

  FIG. 3 represents a formed part 40 ′ with a variant ′ of the star-shaped core of FIG. 2 which in this case covers the edges of the pressed formed part 40. This variant has an advantage because the core in the form of star 20, 20 'is relatively fragile. In the case of the design shown in FIG. 3, the star-shaped core 20 ′ cannot move inside the pre-ceramic formed part 40 ′ and therefore remains

  reliably intact during the entire manufacturing process.

Claims (6)

  1. Process for manufacturing parts made of composite materials   reinforced with fibers from ceramic composite blanks -   fiber-reinforced ceramics, having a porous carbon-based matrix, in which fibers, bundles of fibrous material or fiber agglomerates based on carbon, nitrogen, boron and / or silicon are mixed, with at least one carbonizable binder and possibly other addition materials or fillers to obtain a mass to be pressed and the mass to be pressed is pressed to obtain a blank, which is then pyrolysed, the binder, of which there is at least one, is converting into a matrix based on porous carbon and the raw part, armed with fibers, resulting being infiltrated with a molten metal or silicon, characterized in that to the mass to be pressed at least one metal core is added ( 20, 20 ') made of silicon or a silicon alloy which is introduced to the press in the blank and remains there and serves as a source   of silicon during infiltration by a molten bath.   2. Method of claim 1, characterized in that   that we use a single star-shaped core (20, 20 ').   3. Method according to one of claims I and 2, characterized by the fact   that we use cores (20, 20 ') of pure silicon.   4. Method according to one of claims 1 and 2,   characterized by the fact that silicon-containing cores are used which consist of iron / silicon or aluminum / silicon alloys or mixtures of boron and silicon nitride.   5. Method according to one of the preceding claims,   characterized by the fact that the blank is pressed in a pressing device (10)   having a flying envelope (15).   6. Use of the method according to one of claims 1 to 5 for   manufacture brake discs ventilated from the inside out of materials fiber reinforced composites.